COMMUNAL ROOSTING OF CITY BIRDS

Barn Swallows Roosting in Ratnapura Town 

A roost is a place where a bird rests or sleeps. These would generally, be a perch on a tree or even on buildings in the case of urban habitats. Cliffs or rock faces and other habitats are used as roosts by some birds who have special adaptations. Birds roost when humans retire indoors for the night and this avian behavior goes unnoticed. However, birds roosting in urban habitats have been of concern to the urban dweller for it interferes in his nightly movement.

All terrestrial animals and avian creatures are divided into two groups as diurnal and nocturnal species. The diurnal species take refuge in safe locations during the night and the nocturnal species during the day. This could be shown as the need to rest the anatomical functions especially while vision is not quite sufficient to go about in their routine behavior.

In the case of breeding birds, one bird would sit in the nest taking care of the nestlings or the brood while the other would perch close by. The primary objective of this type of roosting behavior would be for safety, from nocturnal predators. This form of parental roosting is to change totally in the non-breeding season. The non-breeding roosts are generally communal or group roosts.

Most urban roosts are communal while they would vary from single species roosting to mixed-species roosting from time to time in the year. Some ornithological research has been done on these communal roosting in urban habitats and potential reasons have been determined. 

The Galle city in the south of Sri Lanka where I live has a few communal roosting sites in the parks and coconut groves close to the city center. Two decades ago these habitats were dominated by the two crow species, both the Large-billed crow and the House crow. The House crow is abundant in the cities and urban habitats. Crows have been in the habit of frequenting urban areas very much for the ample food sources that were freely available when the meat stalls and fish stalls were in open buildings. These stalls became ample larders throughout the day where meat and fish were prepared and waste collected in open dumps. These open garbage dumps were heavens to scavenge on and the urban crow population increased to unmanageable numbers. The parks and the city sidewalks were no longer leisure areas in the evenings when their droppings littered them, demanding the attention of the local authorities. 

Urban House Crow Populations

However, the last decade shows some significant changes in our urban food usage and the management and disposal of urban waste. The once open meat and fish stalls are now indoors. The supermarket concept where meat and fish are pre-dressed and processed for sale in packed units have come to stay. Open waste dumping is prohibited and is an offense. The bio-degradable garbage is either turned into compost on small home units or delivered to the collecting trucks in an organized manner. These changes have affected the freely available fast-food sources and the result being the decline of the city crow numbers. 

However, the decline in the crow population at roosts made way for other birds into these once crow dominated roosts. Today thousands of Common Mynah birds have invaded these once crow dominated city roosts. The exception being the Mynahs not having a ready source of food available in the city neither do they scavenge nor prefer a carnivorous diet.  There needs to be some special reason for this attraction. The Large-billed crow which used to roost together with the House crow now prefers smaller group roosts or pairing away from these common city roosts.  They prefer to roost on the up-graded city electrical cables that are bundled and are thicker than the old single-line cables. The thicker insulated bundle gives a better hold on their talons for a comfortable roost. 

Common Mynah

Research studies of our local urban roosts have not been conducted in a detailed manner to reason out these changes. However, there are some common reasons derived from research done in other countries that could be applied to local conditions as well.   

Night temperatures inside cities are 5 - 15 degrees Fahrenheit warmer than the surrounding areas, and in a mass gathering of birds touching each other, the temperatures may be favorable to commence the activity fairly early in the morning.  Most roosting avian species require warmth from the morning sun for effective blood circulation, to become active. Birds are thought not to see well in the dark, so sleeping in the city gives the advantage of being able to see a nightly predator, and also the ability to see where to flee safely as the city is illuminated below the roost. Most street lighting is downlit and the area above them is in the dark. 

The Galle ramparts is an ideal location to watch the gathering of House Crow and the Common Mynah flying into the trees in the park opposite the railway station when dusk falls. The chatter of the Mynah and the cawing of the Crows continue with the birds flying from tree to tree looking for the ideal perch possibly sitting on a hierarchical order until it becomes the darkest and to a total quietness.

My presumption is that these crows and mynahs in the city roosts are the younger, immature birds unlike those who have mated for life and roost in pairs in localized roosts. These communal roosts are also a social function where birds challenge each other, find potential mates and communicate with each other their individual or joint experiences.

It is noted that habitat loss requires greater time for foraging and locating food. Roosting together gives an advantage in locating food, as most birds would know where to go at daybreak and the others could follow. The crows leave very early and the Mynahs are late to leave frequenting the cricket ground to pick the grub in the grasses before they fly away to distant feeding grounds.   

Rose-ringed Parakeet

Away from the Galle Town, towards Matara in Katugoda is another communal roost that of the Rose-ringed Parakeet. This again is unique with the coconut trees laden with hundreds of parakeets at sunset. They would stay on the palm fronds until darkness falls to move to the underside of the frond. They have a very peculiar way of roosting in the underside of the palm frond hanging with their feet apart locked in the leaves; some hanging upside down and some keeping upright by holding onto another leaf by the beak. This strange acrobatic roosting method could be explained as a precautionary adaptation to predation from nocturnal owls etc. When hanging from under the palm frond it's completely hidden needing special predatory adaptation.

This roost has now shifted inland with the development of the new Galle Port access roadway connecting to the Southern Highway cutting through this area. The Rose-ringed parakeet being monogamous, the numbers in these communal roosts could also be noted as non-breeding young birds. The more prosperous eligible ones will wait for the lifetime pairing when they would be leaving this community to bring up their young in tree-hole abodes.

There are other special communal roosts in many urban locations in the country. Of them, the millions of barn swallow that roost in the electrical and telegraph wires in the Ratnapura and Pelmadulla towns during the migratory season is unique.